- Ocean Atlantic (1986)
- Oceanos (2001)
- Odeep One (1986)
- Odil (1970)
- Odin (1982)
- Odin Sydfyen (1982)
- Odysseas Elytis (1972)
- Ofelia (1968)
- Okudogo 3 (1976)
- Olau Britannia (1982)
- Olau Britannia (1990)
- Olau Dana (1969)
- Olau Hollandia (1981)
- Olau Hollandia (1989)
- Olau Kent (1970)
- Olau West (1964)
- Olympia (1986)
- Olympus (1976)
- Olympus (1980)
- Ontoseno-I Bsb-II (1971)
- Onyx (1966)
- Optima Seaways (1999)
- Orange (1998)
- Orient Express (1975)
- Ormsö (2015)
- Ornöström (1959)
- Oscar Wilde (1987)
- Oscar Wilde (2007)
- Oscar Wilde (2011)
- Oslofjord (1993)
- Ostend Spirit (1987)
- Ostend Spirit (1992)
- Oster (1971)
- Ottersøy IV (1965)
- Ouzoud (1974)